This proposal is aimed at furthering our understanding of the molecular nature of the interactions of metal centers with four types of biologically important ligands. We will synthesize and examine the chemical properties of complexes of diazenes. Diazenes are unstable species which may be important intermediates in nitrogen fixation and may also be responsible for hemolytic anemia through their interaction with the iron centers in hemoglobin. Studies of the interaction of dioxygen with metal complexes of phenolic compounds will be examined in order to provide a model system for the function of certain dioxygenases. Dioxygenases are involved in amino acid metabolism, and their disfunction is a cause of alkaptonuria, but their mechanism of action remains unknown. The direct interaction of ketonic substrates with coordinated dioxygen has been demonstrated and the further reactions of metal-dioxygen-ketone (or quinone) ternary complexes which can lead to the cleavage of carbon-carbon bonds (like that observed for dioxygenases) will be examined in order to discover the mechanism involved. Metals are usually coordinated to imidazole through a metal nitrogen bond, however recent work indicates that metal carbon bonding to imidazole may be achieved. We will determine if such bonding can occur with iron, cobalt and mercury under biologically relevant conditions and if so what are the chemical and biological consequences. Imidazole coordination is important for the cooperativity in hemoglobin (and to respiration) to the action of the cobalt containing vitamin B12 and to electron transport through cytochromes. Metal carbon bonding of this type may also occur in the interactions of the anti-tumor drug Pt(NH3)2Cl2 and and purines and consequently be important in cancer control. The redox reactions involving molybdenium complexes and quinones and flavins will be investigated in order to study how electron-transfer can occur in molybdoflavin enzymes like xanthine oxidase.